A circulation system, which uses such liquid as water as a refrigerant, is generally known as a circulation system that is used for cooling such a cooling target object as a CPU (Central Processing Unit), an LSI (Large Scale Integration), an inverter and a power semiconductor. In this circulation system, a circulation path is formed using a metal material having high thermal conductivity (e.g. aluminum, copper), and the cooling target object is cooled by circulating the refrigerant through the circulation path using a circulation pump to cause a heat exchange between the cooling target object and the refrigerant.
In the case of using the above circulation system for a vehicle cooling system, a mixed solution (antifreeze solution), which contains ion-exchanged water having little content impurity, an organic solvent having a low freezing point (e.g. ethylene glycol), and an anti-corrosive agent to suppress corrosion of metal material, is used. The refrigerant is normally exchanged by an apparatus manufacturer, automobile manufacturer, maintenance provider or the like, but may be exchanged by the user in some cases, and for this, tap water may be used instead of ion-exchanged water. Tap water contains corrosive factors that corrode metal material, such as chloride ions, metal ions and dissolved oxygen, hence metal material constituting the circulation path may corrode and enter into the tap water, or the corrosive factors that corrode metal material may precipitate inside the circulation path. Further, tap water also contains scale forming factors, such as calcium ions, magnesium ions, ionic silica and dissolved carbon dioxide, hence scales (e.g. calcium carbonate scales, magnesium carbonate scales, silica scales) may form inside the circulation path. As a result, the circulation path is clogged by these corrosion products or scales, which drops the cooling efficiency of the cooling target object, and increases pump load when the circulation system is operated.
In recent years, as the improvement of cooling target objects (e.g. electronic devices, power semiconductors) accelerate, the heating values of such cooling target objects are increasing. Therefore, the circulation path of the circulation system is miniaturized so as to improve the cooling efficiency of the cooling target object. However, if the circulation path is miniaturized, the clogging of the circulation path occurs more easily, even by micro foreign substances (e.g. corrosion products, scales) that mix in, and the clogging of the circulation path leads to a drop in the cooling efficiency of the cooling target object, and an increase in the pump load when the circulation system is operated.
As described above, the foreign substances that enter the medium, such as refrigerant, clog the circulation path and cause various problems, therefore foreign substances in the medium must be efficiently removed.
PTL 1 proposes a method for removing foreign substances in the medium by disposing a detachable filter in the circulation path. Further, PTL 2 proposes a foreign substance removal apparatus in which a foreign substance sedimentation unit is disposed at a position that branches from the circulation path.